Overload device.



H. R. GANFIELD.

OVBRLOAD DEVICE.

APPLIOATION FILED MAR. 22, 1911.

1,074,602. Patented 0013.7,1913.

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ugyuamg W/T/VESSES 7 [1V VE/VTOR t BY ATTORNEY.

UNITED STATES PATENT OFFICE.

HARRY R. CANEIELD, OF CLEVELAND, OHIO, A SSIGNOR TO THE ELECTRICCONTROL- LEE AND MANUFACTURING COMPANY, OF CLEVELAND, OHIO, A CORPORATION OF OHIO.

OVERLOAD DEVICE.

Specification of Letters Patent.

Application filed March 22, 1911. Serial No. 616,104.

T 0 (ill whom it may concern:

Be it known that I, HARRY R. OANFIELD, a citizen of the United States, residing at Cleveland, in the county of Cuyahoga and State of Ohio, have invented new and useful Improvements in Overload Devices, of which the following is a specification.

My invention relates to overload devices, particularly to that type in which a relay or switch ,acts upon an overload in the circuit in which it is connected to cause the circuit to be opened at some point, such as at the contacts of a magnetically operated switch.

One object of my invention is to provide an adjustable overload device which for equal increments of adjustment gives substantially equal increases in the amount of current at which the device operates or trips the circuit-breaker.

Another object is to provide a device which takes up a small amount of room in mounting, and which ischeap to. construct and easily calibrated.

Other objects are set forth in the annexed claims.

To more fully describe my invention I will refer to the following drawings; -in which Figure 1 is. a front view of the overload device, the top portion of which is in section. Fig. 2 is a side elevation and part section. Fig. 3 is a curve of calibration for difierent adjustments of the air gap.

. Referring to Figs. 1 and 2, a C-shaped frame 1, preferab y of magnetic material, is supported by a piece of insulating material 2, such as slate: Within the frame 1 is the armature or core 3 made of magnetic material. Attached to this core is a rod 4 of non-magnetic material, such as brass,

which extends downward through the frame and has at its lower end an insulating bushing 5, which surrounds a reduced section of the rod at A. This bushing is held by means of the nuts 6 against a shoulder of the rod at 4". Loosely mounted upon the bushing is a disk 7 of. conducting material, which rests upon carbon contacts 8 which are in turn supported by the contact studs 9 and held thereon by means of the screws 10. An insulating washer 11 rests upon the disk 7 and a compression spring 12 serves to hold the disk firmly upon the contacts 8. The core 3 andthe rod 4 have a free, or lost,

motion due to the space between the flange of the bushing 5 and the disk 7, so that when thecore 3 is raised, it can move through a small distance without engaging the-disk 7. The force required to move it through this-small distance will depend only upon the weight of theplunger and rod.

After this lost motion-has been taken up,

any further movement of the core 3 will lift the disk 7 oif the cont-acts 8 against the force of the spring 12. An insulating .washer 13 serves to maintain a positive air gap between the core .3 and the lower part of the frame 1, which when the core is in its normal position will always be constant. The core 3 has a guide 14 of non-ma netic material, such as brass, which exten .upward into a plug 15 of magnetic material. This plug is supplied with a coarse pitch thread by which the air gap 16 may be adjusted by turning the adjusting head 17. Around the periphery of the adjusting head 17 are notches and a catch 18 mounted upon the frame holds the head in any desired position. Mounted concentrically with the axis of the core 3 is the winding 19 which is shown of strap copper wound on a central terminal 20 and terminating in the outer terminal 21. These terminals, 20 and 21, have studs :23 projecting through the slate 2 for connecting the circuit conductors. Each turn of the strapwinding is es arated from its adjacent turn by means 0. suitable insulating material 22. 1

'It is evident that the magnetic pull on the upper end of the core increases while the current in the winding 19 increases in direct proportion to the square of the flux.

density, because the magnetic flux is uniform in direction and at right angles to the upper face of the core. At the "lower end of the core, the magnetic lines diverge, the divergence increasing as the flux density increases, so that the component of flux at right angles to the lower surface of the core does not increase as rapidly asthe flux density through the upper'end of the core. In order that the contacts 8, 8 may be lifted, it is necessary that the flux acting on the upper end of the core shall overcome not only the gravity of the core and the parts suspended thereon, and the tension of the spring 12, but also theopposing magnetic .pull acting on the lower end of the core.

The magnetic flux at the lower end of the core is distributed difi'erently than it is where the core has a magnetic portion extending down through the lower arm of the frame, since in the latter construct-ion practically no magnetic pull exists preventing, or tending to prevent, the core from rising. One of the characteristic features of the device described is that both ends of the vertical core lie between the horizontal arms of the magnetic circuit, together with an air gap between the lower end of the core and the lower horizontal arm of the circuit, whereby the total flux has a certain component entering the lower end of the core at right angles to its surface, while the upper end of the core is well within the magnetizing winding, and substantially all of the flux leaves the upper end of the core at right angles to its surface.

By properly proportioning the two air gaps 16, and 13, and with the proper arrangement of them with respect to the winding and the magnetic circuit, it is foundthat for low currents flowing in the winding a force is exerted upon the core 3 tending to hold it down, and that as the value of current in the winding increases a point is reached at which the core will be lifted, and when this action is once started the core 3 will continue to move upward, completely closing the gap 16. By adjusting the position of the plug 15 so that the gap 16 is increased, the value of current at which the core will be lifted is increased, and I have found that by a proper proportioning of the parts, an equal increase of this gap will cause an equal increase in the amount of current required to lift the core 3. I have found that T can obtain a range of adjustment of about 4: to 1 by increasing this air gap 3' to 11-, and by constructing the thread on the plug 15 so that one complete turn will raise the plug through this distance, the total adjustment of the overload device may be obtained by a single turn of the adjusting head 17. Since equal increases of the gap 16 produce equal increases in the current, the overload device may be easily calibrated by obtaining the two positions of the adjusting head for two known values of current at which the device will operate, and the intermediate po sitions can then be marked on the adjusting head by dividing up the interval in equal arbitrary amounts.

In Fig. 3 ll show a curve of calibration X of an overload device in which the ordinates represent the current in amperes flowing in a winding of a certain number of turns, and the abscissae represent the length of the air gap 16 in inches. It will be observed that if the air gap 16 is .3 inches long this particular device will operate at 100 amperes, and if the gap is increased so Love-nos that its length is .5 inches, the current at which the core will lift is 250 amperes, and so on for other adjustments of the air gap. This curve is practically a straight line.

The eflect of varying the gap 13 is to change the shape of the curve of operation shown in Fig. 3; that is to say, the constant ratio between the increase of the gap 16 and the increase in the value of current for operating the device is destroyed if the gap 13 is made substantially greater or less than the size which gives this constant ratio. l have found that by shortening the gap 13 the current curve in Fig. 3 changes from a straight line to one which bends upward at the right-hand end. This tendencyto bend upward increases more and more asthe gap 13 is shortened. Such a curve is shown at Y in Fig. 3. Similarly, if the gap 13.is lengthened, the current curve bends downward at the righthand end. Such a curve is shown at Z in Fig. 3.. It is seen, therefore, that the gap 13 can be made of such a length that the current curve will be between the curves Y and Zand become a straight line, as at X. The length of the washers between the frame and the bottom of the armature 3.

lit will be readily understood by those skilled in the art that the contacts 8, by means of their studs 9 can be :connected to the winding of a magnetically operated circuit breaker which will be caused to open the circuit which flows through its contacts whenever the current in the winding 19 reaches the value for which the device is set to operate,

The movement of the core can also be used to trip an ordinary hand reset circuit breaker.

it do not limit myself to the precise construction as that here shown and described, but I desire to cover such changes therein as do not depart from the spirit of my invention and are within the scope of the appended claims."

ll claim- 1. In a magnetically-operated device, a frame, a movable member, a winding to move said member when energized with predetermined values of current, an air gap between said member and the frame, means for adjusting said air gap in predetermined increments .to change the value of operating current, and means for maintaining substantially constant the ratio between said increments of adjustment and the increments of operating current.

2. In a magnetically-operated device, a

frame, a movable member, a winding to move said member when energized with predetermined values of cnrrent, an air gap Signed at Cleveland, Ohio, this 15th day getwean said member and the frzame; means of March, A. D. 1911.

or a justing seid air p in pre etermined I increments to change i: value of oierating HARRY GANFIELD' 5 current, and means for changing t e ratio Witnesses:

between said increments of adjustment and J. H. HALL, the increments of operating current. M. Dmmm. 

